During open-heart surgery the blood of the patient is bypassed to an extracorporeal support system which supplies the pumping function of the heart and the oxygenation function of the lungs. This effectively isolates the heart enabling the surgeon to make the necessary repairs to the heart. During the surgery it is desirable to arrest the beating/pumping action of the heart. It is also important during the time that the heart is isolated from the blood supply circuit that the heart be protected from ischemia or lack of blood flow which can result in permanent damage to the heart.
It is well known that the heart may be protected during open heart surgery by utilizing a technique commonly known as cold cardioplegia. This involves administering to the heart a cooled cardioplegia fluid which may consist of a crystalloid chemical solution containing potassium and other additives or a mixture of the crystalloid solution with blood. Use of a cooled cardioplegia fluid comprising a mixture of oxygenated blood and crystalloid solution is known to be effective in keeping the heart arrested while at the same time keeping the heart oxygenated. The cardioplegia fluid is cooled by utilizing a cardioplegia delivery system which includes a heat exchanger.
In addition to the cold cardioplegia technique described above, some heart surgeons have more recently begun utilizing a technique called warm continuous blood cardioplegia. In this technique the cardioplegia fluid is not cooled and, consequently, it is not necessary to use a heat exchanger in the cardioplegia delivery system. This technique involves supplying a cardioplegia fluid mixture of warm oxygenated blood and cardioplegia solution throughout the cardiac surgery. This technique has gained acceptance among some surgeons as a safe and effective means of arresting and protecting the heart during surgery.
Whether warm cardioplegia or cold cardioplegia is prescribed by the physician, the manner of administration of the cardioplegia fluid during surgery is similar. Cardioplegia delivery systems include components which supply blood and cardioplegia solution, mix the desired ration of blood/cardioplegia solution and then supply the mixture to the patient's heart. A specific ratio of oxygenated blood with cardioplegia solution containing potassium and other additives, is delivered to the coronary arteries. The term cardioplegia fluid, as used herein, shall mean any ratio of blood to cardioplegia solution and shall include 100% blood or 100% cardioplegia solution. Once the heart is arrested, the delivery system continues to supply the cardioplegia fluid to keep the heart arrested and to deliver oxygen to the myocardium. Pressures and temperatures are monitored to avoid damage to the heart. At the end of the bypass procedure, 100% blood is commonly administered to flush the cardioplegia solution out of the myocardium allowing the heart to be returned to its normal sinus rhythm.
During the process of cardioplegia delivery several problems can arise. First, air bubbles can be created in the cardioplegia fluid. Second, if a line is clamped during the procedure the cardioplegia delivery system may become over pressurized. Thus, it would be highly desirable to provide a cardioplegia delivery device which is able to eliminate air bubbles which are inadvertently admitted into the cardioplegia fluid. It would also be advantageous to provide a cardioplegia delivery device which is able to safely and efficiently react to over pressurization of the system without damaging the components of the system or resulting in loss of losing the patient's blood or cardioplegia solution.
Further, when warm cardioplegia is indicated and prescribed by the physician it is desirable to use a cardioplegia delivery device which does not include a heat exchanger. This results both in a cost savings and in a reduction in priming volume. However, using present delivery devices it is difficult to reconnect the delivery circuit to include a heat exchanger during the course of the surgery if it becomes necessary to cool the heart with the cardioplegia fluid. Therefore, it would be desirable to provide a cardioplegia delivery system that can be used initially without a heat exchanger if warm cardioplegia is indicated and later be converted quickly and easily to include a heat exchanger if cold cardioplegia is indicated during the surgery.